This part of the Manual of Style helps editors to achieve consistency in the use and formatting of numbers, dates, times, measurements, currencies, and coordinates in Wikipedia articles. Consistency in style and formatting promotes clarity and cohesion; this is especially important within an article. The goal is to make the whole encyclopedia easier and more intuitive to use. Try to write so the text cannot be misunderstood, and take account of what is likely to be familiar to readers. The less that readers have to look up definitions, the easier the text will be to understand.

Where this manual provides options, consistency should be maintained within an article unless there is a good reason to do otherwise. The Arbitration Committee has ruled that editors should not change an article from one guideline-defined style to another without a substantial reason unrelated to mere choice of style, and that revert-warring over optional styles is unacceptable.[1] If discussion cannot determine which style to use in an article, defer to the style used by the first major contributor.

General notes

Quotations, titles, etc.

Quotations, titles of books and articles, and similar "imported" text should be faithfully reproduced, even if they employ formats or units inconsistent with these guidelines or with other formats in the same article. If necessary, clarify via [bracketed interpolation], article text, or footnotes.

It is acceptable to change other date formats in the same article to provide consistency, so long as those changes would otherwise be acceptable.

Chronological items

Statements likely to become outdated

Except on pages updated regularly (e.g. current events), terms such as now, soon, currently, and recently should usually be avoided in favor of phrases such as during the 1990s and in August 1969. For future and current events, use phrases such as as of March 2015 or since the beginning of 2010 to signal the time-dependence of the information. Or (for example) {{as of|2015}} will produce the text As of 2015[update] and adds the article to a category flagging it for periodic review. However, do not replace (for example) since the start of 2005 with {{as of|2005}} because some information (the start of 2005) would be lost; advanced features of {{as of}} such as {{as of|2005|alt=since the start of 2005}} can be used in such circumstances.

Time of day

12-hour clock times end with dotted or undotted lower-case a.m. or p.m., or am or pm, preceded by a space (e.g. 2:30p.m. or 2:30pm, not 2:30p.m. or 2:30pm). Hours denoted by a single digit should not have a leading zero (e.g. 2:30p.m., not 02:30p.m.). A hard space (see above) is advisable (2:30&nbsp;pm or {{nowrap|2:30 p.m.}}). Use noon and midnight rather than 12 pm and 12 am; whether midnight refers to the start or the end of a date will need to be specified unless it is clear from the context.

24-hour clock times have no a.m., p.m., noon or midnight suffix. Hours under 10 should have a leading zero (e.g. 08:15). 00:00 refers to midnight at the start of a date, 12:00 to noon, and 24:00 to midnight at the end of a date, but "24" should not be used for the first hour of the next day (e.g. use 00:10 for ten minutes after midnight, not 24:10).

The numerical elements of times-of-day are figures (12:45p.m.) rather than words (twelve forty-five p.m.) though conventional terms such as noon and midnight are acceptable (taking care, with the latter, to avoid possible date ambiguity in constructions such as midnight on July 17).

Time zones

Give dates and times appropriate to the time zone where an event took place. For example, the date of the attack on Pearl Harbor should be December7, 1941 (Hawaii time/​date). Give priority to the place at which the event had its most significant effects; for example, if a hacker based in Japan attacked a Pentagon computer in the US, use the time zone for the Pentagon, where the attack had its effect. In some cases the best solution may be to add the date and time in Coordinated Universal Time (UTC). For example:

Rarely, the time zone in which a historical event took place has since changed; for example, China to 1949 was divided into five time zones, whereas all of modern China is UTC+8. Similarly, the term "UTC" is not appropriate for dates before this system was adopted in 1960[2]; Universal Time (UT) is the appropriate term for the mean time at the prime meridian (Greenwich) when it is unnecessary to specify the precise definition of the time scale. Be sure to show the UTC or offset appropriate to the clock time in use at the time of the event, not the modern time zone, if they differ.

Use "in the year" only where needed for clarity (About 1800ships arrived in the year 1801)

Note to table:

^These formats cannot, in general, be distinguished on sight, because there are usages in which 03-04-2007 represents March4, and other usages in which it represents April3. In contrast there is no common usage in which 2007-04-03 represents anything other than April3.

Consistency

Dates in article body text should all use the same format: She fell ill on 25June 2005 and died on 28June, but not She fell ill on 25June 2005 and died on June28.

Publication dates in an article's citations should all use the same format, which may be:

the format used in the article body text,

an abbreviated format from the "Acceptable date formats" table, provided the day and month elements are in the same order as in dates in the article body, or

the format expected in the citation style being used (however, all-numeric date formats other than yyyy-mm-dd must still be avoided).

For example, a single article might contain one, but only one, of:

Jones, J. (20September 2008)

Jones, J. (September20, 2008)

Jones, J. (20Sep 2008)

(among other possibilities).

Access and archive dates in an article's citations should all use the same format, which may be:

the format used for publication dates in the article,

the format expected in the citation style adopted in the article, or

yyyy-mm-dd

For example, a single article might contain either of the following:

Jones, J. (20Sep 2008)... Retrieved 5Feb 2009.

Jones, J. (20Sep 2008)... Retrieved 2009-02-05.

When a citation style does not expect differing date formats, it is permissible to normalize publication dates to the article body text date format, and/or access/archive dates to either, with date consistency being preferred.

Strong national ties to a topic

Articles on topics with strong ties to a particular English-speaking country should generally use the more common date format for that nation. For the United States, this is month before day; for most others, it is day before month. Articles related to Canada may use either format consistently.

Sometimes the customary format differs from the usual national one: for example, articles on the modern US military use day before month, in accordance with military usage.

Retaining existing format

If an article has evolved using predominantly one format, the whole article should conform to it, unless there are reasons for changing it based on strong national ties to the topic or consensus on the article's talk page.

The date format chosen by the first major contributor in the early stages of an article should continue to be used, unless there is reason to change it based on strong national ties to the topic or consensus on the article's talk page.

Where an article has shown no clear sign of which format is used, the first person to insert a date is equivalent to "the first major contributor".

BC and AD are the traditional ways of referring to this era. BCE and CE are common in some scholarly texts and religious writings. Either convention may be appropriate.

Do not change the established era style in an article unless there are reasons specific to its content. Seek consensus on the talk page before making the change. Open the discussion under a subhead that uses the word "era". Briefly state why the style is inappropriate for the article in question. A personal or categorical preference for one era style over the other is not justification for making a change.

BCE and CE or BC and AD are written in upper case, unspaced, without periods (full stops), and separated from the year number by a space (5BC, not 5BC). It is advisable to use a non-breaking space.

AD may appear before or after a year (AD106, 106AD); the other abbreviations appear after (106CE, 3700BCE, 3700BC).

Do not use CE or AD unless required to avoid ambiguity (e.g. "The Norman Conquest took place in 1066" not 1066CE nor AD1066). On the other hand, "Plotinus was a philosopher living at the end of the 3rd century AD" will avoid unnecessary confusion. Also, in "He did not become king until 55CE" the era marker makes it clear that "55" does not refer to his age. Alternatively, "He did not become king until the year 55."

Use either the BC–AD or the BCE–CE notation consistently within the same article. Exception: do not change direct quotations, titles, etc.

Uncalibrated (bce) radiocarbon dates: Some source materials will indicate whether a date is calibrated or not simply by a change in capitalisation; this is often a source of confusion for the unwary reader. Do not give uncalibrated radiocarbon dates (represented by the lower-case bce unit, occasionally bc or b.c. in some sources), except in directly quoted material, and even then include a footnote, a square-bracketed editor's note [like this], or other indication to the reader what the calibrated date is, or at least that the date is uncalibrated. Calibrated and uncalibrated dates can diverge surprisingly widely, and the average reader does not recognise the distinction between bce and BCE or BC.

BP: In scientific and academic contexts, BP (before present) is often used. This is calibrated from January 1, 1950, not from the date of publication, though the latter introduces an insignificant error when the date is distant or an approximation (18,000BP). BP years are given as 18,000BP or spelled out as 18,000years before present (not 18,000YBP, 18,000 before present, 18,000 years before the present, or similar). Do not convert other notations to or from BP unless you are certain of what you are doing. A safer and simpler alternative may be to use "ya (years ago)".

Other era systems may be appropriate in an article. In such cases, dates should be followed by a conversion to Dionysian (or vice versa) and the first instance should be linked: "Qasr-al-Khalifa was built in 221AH (836CE)" or "in 836AD (221AH)".

Astronomical year numbering follows the Common Era and does not require conversion, but the first instance of a non-positive year should still be linked: "The March equinox passed into Pisces in year −67."

Julian and Gregorian calendars

A date can be given in any appropriate calendar, as long as it is (at the minimum) given in the Julian calendar or the Gregorian calendar or both, as described below. For example, an article on the early history of Islam may give dates in both Islamic and Julian calendars. Where a calendar other than the Julian or Gregorian is used, the article must make this clear.

Dates before 15October 1582 (when the Gregorian calendar was adopted) are normally given in the Julian calendar. The Julian day and month should not be converted to the Gregorian calendar, but the start of the Julian year should be assumed to be 1January (see below for more details).

Dates for Roman history before 45BC are given in the Roman calendar, which was neither Julian nor Gregorian. When (rarely) the Julian equivalent is certain, it may be included.

For dates in early Egyptian and Mesopotamian history, Julian or Gregorian equivalents are often uncertain. Follow the consensus of reliable sources, or indicate their divergence.

The dating method used should follow that used by reliable secondary sources (or if reliable sources disagree, that used most commonly, with an explanatory footnote).

At some places and times, the new year began on a date other than 1January. For example, in England and its colonies until 1752, the year began on Annunciation Day, 25March; see the New Year article for other styles. In writing about historical events, however, years should be assumed to have begun on 1January (see the example of the execution of Charles I in "Differences in the start of the year"); if there is reason to use another start-of-year date, this should be noted.

If there is a need to mention Old or New Style dates in an article (as in the Glorious Revolution), a footnote should be provided on the first usage, stating whether the New Style refers to a start of year adjustment or to the Gregorian calendar (it can mean either).

Ranges

A pure year–year range is written (as is any range) using an en dash (&ndash; or {{ndash}}), not a hyphen or slash; this dash is usually unspaced (that is, with no space on either side); and the range's "end" year is usually abbreviated to two digits:

Periods straddling two different years, including sports seasons, are generally written with the range notation (2005–06). The slash notation (2005/06) may be used to signify a fiscal year or other special period, if that convention is used in reliable sources.

A date range may appear in 2005–2010 format if it is a range of sports seasons in an infobox.[8] This format is also indicated for date ranges appearing in reference citations if any dates (of publication, access, archival) are in YYYY-MM-DD format, because the range in question could thus be easily mistaken for a yyyy-mm date: XYZ Annual Review, 2005–2006. Accessed 2013-04-07. but not XYZ Annual Review, 2005–06. Accessed 2013-04-07. Another case is in tables (and lists the items of which begin with date ranges) in which some but not all date ranges span a century (sortability of a date column in a table also requires a consistent format for all entries: 2005–07 will unintentionally sort before 2005–2006).

Other "pure" ranges use an unspaced en dash as well:

day–day: 5–7January 1979;January5–7, 1979;elections were held March 5–8

month–month: the 1940 peak period was May–July;the peak period was May–July 1940; (but the peak period was May 1940 – July 1940 uses a spaced en dash—​see below)

If at least one of the items being linked is in a "mixed" format (containing two or more of day, month, year), carries a modifier such as c., or otherwise contains a space, then a spaced en dash ({{snd}}) is used:

When a person is known to have been active ("flourishing") during certain years, fl., [[floruit|fl.]], or {{fl.}} may be used:

• Osmund (fl. 760–772)...

• Aethelwalh (fl. c. 660 – 685)...

The linked forms should not be used on disambiguation pages, and "active" followed by the range is a better alternative for artists, soldiers and other persons with an occupation.

When a date is known to be either of two years (e.g. from a regnal or AH year conversion, or a known age at death):

• Anne Smith (born 1912 or 1913; died 2013)...

Other forms of uncertainty should be expressed in words, either in article text or in a footnote: April14, 1224 (unattested date). Do not use a question mark (1291?) for such purposes, as this fails to communicate the nature of the uncertainty.

Other periods

Days of the week

Days of the week are capitalized (Sunday, Wednesday).

Seasons

Seasons are uncapitalized (a hot summer) except when personified: Soon Spring will show her colors; Old Man Winter.

Using seasons to refer to a particular time of year (winter 1995) is ambiguous, because northern and southern hemisphere seasons are six months out of phase, and many areas near the equator instead have wet and dry seasons. Consider alternative phrasing: early 1995;the first quarter of 1995;January to March 1995; spent the southern summer in Antarctica.

However, using seasons is appropriate when referring to seasonal events: the autumn harvest;migration typically begins in mid-spring.

Decades

To refer to a decade as a chronological period per se (not with reference to a social era or cultural phenomenon) always use four digits (the1980s, but not the1980's or the1980‑ies, and definitely not the1980s').

Prefixes should be hyphenated (themid‑1980s;pre‑1960s social attitudes).

For a social era or cultural phenomenon associated with a particular decade:

Two digits (with a preceding apostrophe) may be used as an alternative to four digits, but only if this is a well-established phrase seen in reliable sources (theRoaring'20s,theGay'90s,condemning the '60s counterculture, but grew up in 1960s Boston, moving to Dallas in1971, and do not write the90's;the90s; or the90s').

A third alternative (where seen in reliable sources) is to spell the decade out, capitalized: changing attitudes of the Sixties

Centuries and millennia

Treat the 1st century AD as years 1–100, the 17th century as 1601–1700, and the second millennium as 1001–2000; similarly, the 1st century BC/BCE was 100–1 BC/BCE, the 17th century was 1700–1601 BC/BCE, and the second millennium 2000–1001 BC/BCE.

The 18th century (1701–1800) and the 1700s (1700–1799) are not the same period.

When using forms such as the 1700s ensure there is no ambiguity as to whether e.g. 1700–1709, or 1700–1799, is meant.

Note that the sequence of years runs ...2BC, 1BC, 1AD, 2AD...—​there is no "year 0".

Centuries and millennia are identified using either figures (the 18thcentury, not XVIII century) or words (the second millennium). When used adjectivally they contain a hyphen (nineteenth-century painting or 19th-century painting). Do not capitalize (the best Nineteenth-century paintings;during the Nineteenth Century).

Abbreviations for long periods of time

When the term is frequent, combine the abbreviations "yr" for "years" and "ya" for "years ago" with prefixes "k" for "thousand" (kya, kyr), "m" for "million" (mya, myr), and "b" for "billion" (bya, byr).

In academic contexts, annum-based units are often used: "ka" (kiloannum), "Ma" (megaannum) and "Ga" (gigaannum). Some authorities, such as the British Museum, simply spell out "years ago".

For any of these abbreviations, show the meaning parenthetically on first occurrence and again where use is extensive,[clarification needed] or might be a standalone topic of interest. For source quotations use square brackets, as in "a measured Libby radiocarbon date of 35.1mya [million years ago] required calibration ..."

Numbers

Numbers as figures or words

See also information on specific situations, elsewhere in this guideline.

Generally, in article text:

Integers from zero to nine are spelled out in words

Integers greater than nine expressible in one or two words may be expressed either in numerals or in words (16 or sixteen, 84 or eighty-four, 200 or two hundred). In spelling out numbers, "components" from 21 to 99 are hyphenated; larger ones are not (fifty-six, five hundred).

Other numbers are given in numerals (3.75, 544) or in forms such as 21million. Markup:21{{nbsp}}million

billion and trillion are understood to represent their short-scale values of 109(1,000,000,000) and 1012(1,000,000,000,000), respectively.

M (unspaced) and bn (unspaced) may be used for million and billion after spelling out the first occurrence (e.g. She received £70 million and her son £10M).

SI prefixes and symbols, such as giga-(G) and tera- (T), should be restricted to use in scientific and engineering expressions.

Sometimes, the variety of English used in an article may necessitate the use of a numbering system other than the Western thousands-based system. For example, the South Asian numbering system is convention­ally used in South Asian English. In those situations, link the first spelled-out instance of each quantity (e.g. [[crore]], which yields crore). (If no instances are spelled out, provide a note after the first instance directing the reader to the article about the numbering system.) Also, provide a conversion to Western numbers for the first instance of each quantity, and provide conversions for subsequent instances if they do not overwhelm the content of the article. For example, write three crore (thirty million). Group digits in Western thousands-based style (e.g., 30,000,000; not 3,00,00,000): see § Delimiting (grouping of digits) below. (Note that the variety of English does not uniquely determine the method of numbering in an article. Other considerations, such as conventions used in mathematics, science and engineering, may also apply, and the choice and order of formats and conversions is a matter of editorial discretion and consensus.)

In tables and infoboxes, quantities are expressed in figures (Years in office:5); but numbers within a table's explanatory text and comments follow the general rule.

Numbers in mathematical formulae are never spelled out (3<π<22/7, not three < π < 22 sevenths).

Comparable quantities should be all spelled out or all in figures:

• five cats and thirty-two dogs, not five cats and 32 dogs.

• 86men and 103women, not eighty-six men and 103 women

• There were 3 deaths and 206 injuries (even though 3 would normally be given as three) or Three died and two hundred six were injured (even though two hundred six would normally be given as 206), not There were three deaths and 206 injuries

But adjacent quantities not comparable should usually be in different formats:twelve 90-minute volumes or 12 ninety-minute volumes, not 12 90-minute volumes or twelve ninety-minute volumes.

Avoid awkward juxtapositions: On April 28, 2006, thirty-one more died., not On April 28, 2006, 31 more died.

Sometimes figures and words carry different meanings; for example Every locker except one was searched implies there is a single exception (we don't know which), while Every locker except 1 was searched means that Locker 1 (only) was not searched.

• Not There were many attacks. 23 men were killed, but There were many attacks; 23men were killed or There were many attacks. Twenty-three men were killed.

• Not 1945 and 1950 saw crucial elections (nor Nineteen forty-five and 1950 saw crucial elections – because comparable numbers should be both written in words or both in figures) but The elections of 1945 and 1950 were crucial.

Exception: Where a proper name, technical term, etc., itself beginning with a numeral, opens the sentence (1-Naphthylamine is typically synthesized via the Felden­shlager–Glocken­spiel process) although this can usually be avoided by rewording (Felden­shlager–Glocken­spiel is the process typically used in the synthesis of 1-Naphthylamine).

Fractions

Where numerator and denominator can each be expressed in one word, a fraction is usually spelled out (e.g. a two-thirds majority); use figures if they occur with an abbreviated unit (e.g. 1⁄4yd—markup:{{frac|1|4}}&nbsp;yd, not a quarter of a yd or a quarter yd).

Mixed numbers are usually given in figures, unspaced (not Fellini's film 81⁄2 or 8-1⁄2 but Fellini's film 81⁄2—markup:{{frac|8|1|2}}). In any case the integer and fractional parts should be consistent (not nine and1⁄2).

Non-metric (imperial and US customary) measurements may use fractions or decimals (51⁄4inches;5.25inches); the practice of reliable sources should be followed, and within-article consistency is desirable.

In science and mathematics articles mixed numbers are rarely used (not 11⁄3 times the original voltage, but 4/3 the original) and use of {{frac}} is discouraged in favor of one of these styles:

Decimals

A period/full stop (never a comma) is used as the decimal point (6.57, not 6,57).

The number of decimal places should be consistent within a list or context (The response rates were 41.0 and 47.4 percent, respectively, not 41 and 47.4 percent), unless different precisions are actually intended.

Numbers between −1 and +1 require a leading zero (0.02, not .02); exceptions are sporting performance averages (.430 batting average) and commonly used terms such as .22caliber.

Nouns following a number expressed as a decimal are plural (averaging 0.7 years).

Indicate repeating digits with an overbar e.g. 14.31{{overline|28}} gives 14.3128. (Consider explaining this notation on first use.) Do not write e.g. 14.31(28) because it resembles notations for § Uncertainty.

Grouping of digits

Left of the decimal point: Five or more digits should be grouped (and exactly four digits may optionally be grouped) into triples separated by commas (never period/full stop): 12,200;255,200;8,274,527;1,250 (optionally 1250).

Exception: never group four-digit page numbers or four-digit calendar years (not sailed in 1,492, though 10,400BC).

In scientific/engineering articles, long strings left of the point may be grouped into triples without commas: 8274527

Right of the decimal point: Five or more digits may be grouped into triples without commas: 99.123456.

In mathematics-oriented articles, digits right of the point may be grouped into fives: 3.14159265358979323846....

Delimiting style should be consistent throughout a given article.

Markup: Templates {{val}}, {{val/delimitnum}}, {{gaps}}, and {{gapnum}} may be useful in grouping digits. Use of hard-coded spaces, such as the regular space character, the non-breaking space (&nbsp; or {{space}}), and the thin space (&thinsp; or {{thinsp}}), is problematic for screen readers because they read out each group of digits as separate numbers (e.g. 30 000 is read as "thirty zero zero zero").

Percentages

In the body of non-scientific/non-technical articles, percent (American English) or per cent (British English) are commonly used: 10 percent; ten percent; 4.5 per cent. Ranges are written ten to twelve per cent or ten to twelve percent, not ten–twelve per cent or ten to twelve %.

In the body of scientific/​technical articles, and in tables and infoboxes of any article, the symbol % (unspaced) is more common: 71%, not 71 % or three %. Ranges: 10–12%, not 10%–12% or 10 to 12%.

When expressing the difference between two percentages, do not confuse a percentage change with a change in percentage points.

Scientific and engineering notation

Scientific notation always has a single nonzero digit to the left of the point: not 60.22×1022, but 6.022×1023.

Engineering notation is similar, but adjusted so that the exponent is a multiple of three: 602.2×1021.

In a table column (or other presentation) in which all values can be expressed with a single power of 10, consider giving e.g. × 107 once in the column header, and omitting it in the individual entries. (Markup:&times;&nbsp;10{{sup|7}})

In both notations, the number of digits indicates the precision. For example, 5×103 means rounded to the nearest thousand; 5.0×103 to the nearest hundred; 5.00×103 to the nearest ten; and 5.000×103 to the nearest unit.

• Polls estimated Jones's share of the vote would be 55%, give or take about 3%

Markup:{{+-}}, {{su}}, and {{val}} may be used to format uncertainties.

Where explicit uncertainty is unavailable (or is unimportant for the article's purposes) round to an appropriate number of significant digits; the precision presented should usually be conservative. Precise values (often given in sources for formal or matter-of-record reasons) should be used only where stable and appropriate to the context, or significant in themselves for some special reason.

• The speed of light is defined to be 299,792,458m/s

butParticle velocities eventually reached almost two-thirds the 300million m/s speed of light

• The city's 1920 population was 667,000. (not population was 666,666—​an official figure unlikely to be accurate at full precision)

butThe town was ineligible because its official census figure (9,996) fell short of the statutory minimum of ten thousand. (Unusual case in which the full-precision official population figure is helpful to readers.)

• The accident killed 337 passengers and crew, and three airport workers. (Likely that accurate and precise figures were determined.)

• At least 800 persons died in the ensuing mudslides. (Unlikely that any precise number can be accurate, even if an official figure is issued.)

orOfficials listed 835 deaths, but the Red Cross said dozens more may have gone unreported. (In reporting conflicting information, give detail sufficient to make the contrast intelligible.)

• The jury's award was $8.5million (where the actual figure was $8,462,247.63) – reduced on appeal to $3,000,001 (one dollar in actual damages, the remainder in punitive damages).

It may sometimes be appropriate to note the lack of uncertainty information, especially where such information is normally provided and necessary for full interpretation of the figures supplied.

• A local newspaper poll predicted 52% of the vote would go to Smith, but did not publish information on the uncertainty of this estimate.

The {{undue precision}} template may be added to figures appearing to be overprecise.

Avoid using "approximately", "about" and similar terms with figures that have merely been approximated or rounded in a normal and expected way, unless the reader might otherwise be misled.

• The tallest player was 6 feet 3 inches (not ... about 6 feet 3 inches—​heights are conventionally reported only to the nearest inch, even though greater precision may be available in principle).

butThe witness said the assailant was about 5 feet 8 inches tall (about because here the precise value is unknown, with substantial uncertainty).

The reader may be assumed to interpret large round numbers (100,000 troops) as approximations. Writing a quantity in words (one hundred thousand troops) can further emphasize its approximate nature.

In computer-related articles, use the C programming language prefixes 0x (zero-ex) for hexadecimal and 0 (zero) for octal. For binary, use 0b. Explain these prefixes in the article's introduction or on first use.

In all other articles, use <sub> to create subscripts: 1379, 2413. Markup:137<sub>9</sub>, 241<sub>3</sub>

For bases above 10, use symbols conventional for that base (as seen in reliable sources) e.g. for base 16 use 0–9A–F.

Units of measurement

Unit choice and order

Quantities are typically expressed using an appropriate "primary unit", displayed first, followed by a conversion in parentheses, when appropriate, e.g. 200 kilometres (120 mi). For details on when and how to provide a conversion, see the section § Unit conversions. The choice of primary units depends on the circumstances, and should respect the principle of "strong national ties", where applicable:

In non-scientific articles relating to the United States, the primary units are US customary, e.g. 97pounds (44kg).

In non-scientific articles relating to the United Kingdom, the primary units for most quantities are metric or other internationally used units,[10] except that:

the primary units for distance/​length, speed and fuel consumption are miles, miles per hour, and miles per imperial gallon (except for short distances or lengths, where miles are too large for practical use);

the primary units for personal height and weight are feet​/inches and stones/​pounds;

imperial pints are used for quantities of draught beer/​cider and bottled milk;

UK engineering-related articles, including all bridges and tunnels, generally use the system of units that the topic was drawn-up in (but road distances are given in imperial units, with a metric conversion).

Special considerations:

Quantities set via definition (as opposed to measured quantities) should be given first in the units used in the definition, even if this makes the structure of presentation inconsistent: During metrification, the speed limit was changed from 30miles per hour (48kilometers per hour) to 50km/h (31mph).

This may benefit from a slightly non-standard structure, such as ...from 30miles per hour (about 48kilometers per hour) to 50km/h (about 31mph). In this sort of case, using "about" can help make clear which is the statutory, exact value.

Nominal quantities (e.g. "2 × 4" lumber) require consideration of whether the article is concerned with the item's actual dimensions or merely with its function. In some cases only the nominal quantity may suffice; in others it may be necessary to give the nominal size (often in non-SI units), the actual size in non-SI units, and the actual size in SI units.

Whenever a conversion is used, ensure that the precision of the converted quantity in the article is comparable to the precision of the value given by the source (see § Unit conversions).

Where the article's primary units differ from the units given in the source, the {{convert}} template's |order=flip flag can be used; this causes the original unit to be shown as secondary in the article, and the converted unit to be shown as primary.

Unit names and symbols

Definitions:

Examples of unit names: foot, meter, kilometer.

Examples of unit symbols: ft, m, km.

Unit names and symbols should follow the practice of reliable sources.

In prose, unit names should be given in full if used only a few times, but symbols may be used when a unit (especially one with a long name) is used repeatedly, after spelling out the first use (e.g. Up to 15kilograms of filler is used for a batch of 250kg).

Certain unit names (e.g. °C) need never be written in full unless required stylistically (automatic conversion of degrees Celsius to degrees Fahrenheit).

Where space is limited, such as in tables, infoboxes, parenthetical notes, and mathematical formulas, unit symbols are preferred.

Units unfamiliar to general readers should be presented as a name–symbol pair (Energies were originally 2.3megaelectronvolts (MeV), but were eventually 6MeV).

Ranges use unspaced {{ndash}} if only one unit symbol is used at the end (e.g. 5.9–6.3kg), and spaced en dash ({{snd}}) if two symbols are used (e.g. 3μm – 1mm); ranges in prose may be specified using either unit symbol or unit names, and units may be stated either after both numerical values or after the last (e.g. from 5.9 to 6.3kilograms, from 5.9kilograms to 6.3kilograms, from 5.9 to 6.3kg and from 5.9kg to 6.3kg are all acceptable).

Length–width, length–width–height and similar dimensions may be separated by the multiplication sign (×) or the word by.

With the multiplication sign, each number should be followed by a unit name or symbol (if appropriate):

Unit names are given in lower case except: where any word would be capital­ized; where otherwise specified in the SI brochure; where otherwise specified in this Manual of Style.[clarification needed]

He walked several miles.

Miles of trenches were dug.

A Gallon equals 4 Quarts.

Except as listed in the "Specific units" table below, unit symbols are uncapi­tal­ized unless they are derived from a proper name, in which case the first letter (of the base unit symbol, not of any prefix) is capitalized.[11]

8 kg

100 kPa

8 Kg

100 kpa

Unit symbols are undotted.

38 cm

38 cm.

Except as shown in the "Specific units" table below, a space appears between a numeric value and a unit name or symbol. In the case of unit symbols, &nbsp; (or {{nowrap}}‍) should be used to prevent linebreak.

29kgMarkup:29&nbsp;kg

29kg

To form a value and a unit name into a compound adjective use a hyphen or hyphens...

a five-day holiday

a five-cubic-foot box

a 10-centimeter blade

... but a non-breaking space (never hyphen) separates a value and unit symbol.

a blade 10 cm long

a 10-cm blade

Plurals

SI unit names are pluralized by adding s or es...

1 ohm, 10 ohms

... except for these irregular forms.

1 henry, 10 henries

1 hertz, 10 hertz

1 lux, 10 lux

1 siemens, 10 siemens

10 henrys

10 hertzes

10 luxes

Some non-SI units have irregular plurals.

1 foot, 10 feet

1 stratum, 10 strata (unusual)

10 foots

10 stratums

Unit symbols (in any system) are identical in singular and plural.

grew from 1 in to 2 in

grew from 1 inch to 2 inches

grew from one to two inches

grew from 1 in to 2 ins

Powers

Format exponents using <sup>, not special characters.

km2Markup:km<sup>2</sup>

km²Markup:km&#178;

Or use squared or cubed (after the unit being modified).

ten metres per second squared

ten metres per squared second

For areas or volumes only, square or cubic may be used (before the unit being modified).

ten metres per square second

grams per square centimeter

The abbreviations sq and cu may be used for US customary and imperial units but not for SI units.

15sqmi

3cuft

15sqkm

3cum

Products

Indicate a product of unit names with either a hyphen or a space.

foot-pound

foot pound

footpound

foot·pound

Indicate a product of unit symbols with &middot; or &nbsp; (Note:{{middot}} is not equivalent to &middot;.)

ms = millisecond

m·s or ms = metre-second.

Exception: In some topic areas such as power engineer­ing, certain products take neither space nor &middot;. Follow the practice of reliable sources in the article's topic area.

US or imperial/imp must be specified; fluid/fl must be specified, except withgallon. (Without fluid, ounce is ambiguous – versus avoirdupois ounce or troy ounce – and pint or quart is ambiguous – versus US dry pint or US dry quart.)

imperial fluid pint

imp fl pt

imperial fluid quart

imp fl qt

imperial gallon

imp gal

US fluid ounce

US fl oz

US fluid pint

US fl pt

US fluid quart

US fl qt

US gallon

US gal

cubic foot

cu ft (notcf)

Write five million cu ft or 5,000,000cuft, not 5MCF.

cubic foot per second

cu ft/s (notcfs)

litre

liter (U.S.)

lorL

The symbol l in isolation (i.e. not in such forms as ml) is easily mistaken for the digit 1.

A measure of purity for gold alloys. (Do not confuse with the unit of mass with the same spelling.)

Time

second

s

Do not use &prime; (′), &Prime; (″), apostrophe (') or quote (") for minutes or seconds. Use m for minute only where there is no danger of confusion with meter, as in the hours–minutes–seconds formats for time durations described in the Unit names and symbols table.

minute

min

hour

h

year

a

Use a only with an SI prefix (a rock formation 540Maold, not Life expectancy rose to 60 a).

In certain subject areas calorie is convention­ally used alone. Articles following this practice should specify on first use whether the use refers to the small calorie or to the kilocalorie (large calorie). Providing conversions to SI units (usually calories to joules or kilocalories to kilojoules) may also be useful. A kilocalorie (kcal) is 1000 calories. A calorie (small calorie) is the amount of energy required to heat 1 gram of water by 1 °C. A kilocalorie is therefore also a kilogram calorie.

Quantities of bytes and bits

In quantities of bits and bytes, the prefixes kilo (symbol k or K), mega (M), giga (G), tera (T), etc. are ambiguous. They may be based on a decimal system (like the standard SI prefixes), meaning 103, 106, 109, 1012, etc., or they may be based on a binary system, meaning 210, 220, 230, 240, etc. The binary meanings are more commonly used in relation to solid-state memory (such as RAM), while the decimal meanings are more common for data transmission rates, disk storage and in theoretical calculations in modern academic textbooks.

Follow these recommendations when using these prefixes in Wikipedia articles:

Following the SI standard, a lower-case k should be used for "kilo-" whenever it means 1000 in computing contexts, whereas a capital K should be used instead to indicate the binary prefix for 1024 according to JEDEC. (If, under the exceptions detailed further below, the article otherwise uses IEC prefixes for binary units, use Ki instead).

Do not assume that the binary or decimal meaning of prefixes will be obvious to everyone. Explicitly specify the meaning of k and K as well as the primary meaning of M, G, T, etc. in an article ({{BDprefix}} is a convenient helper). Consistency within each article is desirable, but the need for consistency may be balanced with other considerations.

The definition most relevant to the article should be chosen as primary for that article, e.g. specify a binary definition in an article on RAM, decimal definition in an article on hard drives, bit rates, and a binary definition for Windows file sizes, despite files usually being stored on hard drives.

Where consistency is not possible, specify wherever there is a deviation from the primary definition.

Disambiguation should be shown in bytes or bits, with clear indication of whether in binary or decimal base. There is no preference in the way to indicate the number of bytes and bits, but the notation style should be consistent within an article. Acceptable examples include:

Avoid inconsistent combinations such as A 64MB (67,108,864-byte) video card and a 100GB (100 × 10003-byte) hard drive. Footnotes, such as those seen in Power Macintosh 5500, may be used for disambiguation.

Unless explicitly stated otherwise, one byte is eight bits (see History of byte).

The IEC prefixeskibi-, mebi-, gibi-, etc. (symbols Ki, Mi, Gi, etc.) are rarely used, even in technical articles, so are generally not to be used except:[12]

when the majority of cited sources on the article topic use IEC prefixes,

in a direct quote using the IEC prefixes,

when explicitly discussing the IEC prefixes,

in articles in which both types of prefix are used with neither clearly primary, or in which converting all quantities to one or the other type would be misleading or lose necessary precision, or declaring the actual meaning of a unit on each use would be impractical.

Unit conversions

Where English-speaking countries use different units for the same quantity, follow the "primary" quantity with a conversion in parentheses: the Mississippi River is 2,320 miles (3,734 km) long; the Murray River is 2,375 kilometres (1,476 mi) long. In science-related articles, however, supplying such conversion is not required unless there is some special reason to do so.

Where an imperial unit is not part of the US customary system, or vice-versa—​and in particular, where those systems give a single term different definitions—​a double conversion may be appropriate: Rosie weighed 80 kilograms (180 lb; 12 st 8 lb) (markup: {{convert|80|kg|lb stlb}}); The car had a fuel economy of 5 L/100 km (47 mpg-US; 56 mpg-imp) (markup: {{convert|5|L/100km|mpgus mpgimp|abbr=on}}).

Generally, conversions to and from metric units and US or imperial units should be provided, except:

When inserting a conversion would make a common or linked expression awkward (The four-minute mile).

When units are part of the subject of a topic—​nautical miles in articles about the history of nautical law (5 nautical miles), SI units in scientific articles (a 600-kilometer asteroid), yards in articles about American football—​it can be excessive to provide conversions every time a unit occurs. It could be best to note that this topic will use the units (possibly giving the conversion factor to another familiar unit in a parenthetical note or a footnote), and link the first occurrence of each unit but not give a conversion every time it occurs.

Converted quantity values should use a level of precision similar to that of the source quantity value, so the Moon is 380,000kilometres (240,000mi) from Earth, not (236,121mi). Small numbers may need to be converted to a range where rounding would cause a significant distortion, so one mile (1–2km), not one mile (2km). Be careful especially when your source has already converted from the units you're now converting back to. This may be evidenced by multiples of common conversion factors in the data, such as 160 km (from 100 miles). See false precision.

In a direct quotation, always retain the source units. Any conversions can be supplied either in the quote itself (in square brackets, following the original measurement) or in a footnote. See footnoting and citing sources.

{{Units attention}} may be added to articles needing general attention regarding choice of units and unit conversions.

Currency symbols

In general, the first mention of a particular currency should use its full, unambiguous signifier (e.g. A$52), with subsequent references using just the appropriate symbol (e.g. $88), unless this would be unclear. Exceptions:

In an article referring to multiple currencies represented by the same symbol (e.g. the dollars of the US, Canada, Australia, New Zealand, and other countries – see Currency symbols § dollar variants) use the full signifier (e.g. US$, A$) each time, except (possibly) where a particular context makes this both unnecessary and undesirable.

In articles entirely on EU-, UK- and/or US-related topics, all occurrences may be shortened (€26, £22 or $34), unless this would be unclear.

The pound sterling is represented by the £ symbol, with one horizontal bar. The double-barred ₤ symbol is ambiguous, as it has also been used for the Italian lira and other currencies. For non-British currencies that use pounds or a pound symbol (e.g. the Irish pound, IR£) use the symbol convention­ally preferred for that currency.

Formatting

Do not place a currency symbol after the accompanying numeric figures (e.g. 123$, 123£, 123€) unless that is the normal convention for that currency when writing in English.[clarification needed] Never use forms such as $US123 or $123 (US).

Currency abbreviations that come before the numeric value are unspaced if they consist of a nonalphabetic symbol only, or end in a symbol (£123;€123); but spaced if alphabetic (R75).

Ranges should be expressed giving the currency signifier just once: $250–300, not $250–$300.

million and billion should be spelled out on first use, and (optionally) abbreviated M or bn (both unspaced) thereafter: She received £70 million and her son £10M; the school's share was $250–300 million, and the charity's $400–450M.

In general, a currency symbol should be accompanied by a numeric amount e.g. not He converted his US$ to A$ but He converted his US dollars to Australian dollars or He exchanged the US$100 note for Australian dollars.

Exceptions may occur in tables and infoboxes where space is limited e.g. Currencies accepted for deposit:US$, SFr, GB£, €. It may be appropriate to wikilink such uses, or add an explanatory note.

Conversions

Conversions of less-familiar currencies may be provided in terms of more familiar currencies—​such as the US dollar, euro or pound sterling—​using an appropriate rate (which is often not the current exchange rate). Conversions should be in parentheses after the original currency, rounding to avoid false precision (two significant digits is usually sufficient, as most exchange rates fluctuate significantly), with at least the year given as a rough point of conversion rate reference; e.g. Since 2001 the grant has been 10,000,000 Swedish kronor ($1.4M, €1.0M, or £800k as of August 2009[update]), not ($1,390,570, €971,673 or £848,646).

For obsolete currencies, provide an equivalent (formatted as a conversion) if possible, in the modern replacement currency (e.g. decimal pounds for historical pre-decimal pounds-and-shillings), or a US-dollar equivalent where there is no modern equivalent.

In some cases it may be appropriate to provide a conversion accounting for inflation or deflation over time. See {{Inflation}} and {{Inflation-fn}}.

Geographical coordinates on Earth should be entered using a template to standardise the format and to provide a link to maps of the coordinates. As long as the templates are adhered to, a robot performs the functions automatically.

{{coord}} offers users a choice of display format through user styles, emits a Geo microformat, and is recognised (in the title position) by the "nearby" feature of Wikipedia's mobile apps and by external partners such as Google (-Maps and -Earth) and Yahoo.

Generally, the larger the object being mapped, the less precise the coordinates should be. For example, if just giving the location of a city, precision greater than 100meters is not needed unless specifying a particular point in the city, for example the central administrative building. Specific buildings or other objects of similar size would justify precisions down to 10meters or even one meter in some cases (1′′ ~15m to 30m, 0.0001° ~5.6m to 10m).

The final field, following the E/W, is available for attributes such as type, region and scale.

When adding coordinates, please remove the {{coord missing}} tag from the article, if present.

Notes and references

^See CCTF/09-32: Coordinated Universal Time (UTC). BIPM. n.d. Retrieved on 2015-03-05 (UTC).[1] – On page 3: "This coordination began on January 1, 1960, and the resulting time scale began to be called informally 'Coordinated Universal Time.'"

^All-numeric yyyy-mm-dd dates might be assumed to follow the ISO 8601 standard, which mandates the Gregorian calendar. Also, technically all must be four-digit years, but Wikipedia is unlikely to ever need to format a far-future date beyond the year 9999.

^The number in parentheses is the numerical value of the standard uncertainty referred to the corresponding last digits of the quoted result – see NIST – Use of concise notation

^If there is disagreement about the primary units used in a UK-related article, discuss the matter on the article talk-page, at MOSNUM talk, or both. If consensus cannot be reached, refer to historically stable versions of the article and retain the units used in these as the primary units. Note the style guides of British publications such as The Times (see archived version, under "Metric").

^Wikipedia follows common practice regarding bytes and other data traditionally quantified using binary prefixes (e.g. mega- and kilo-, meaning 220 and 210 respectively) and their unit symbols (e.g. MB and KB) for RAM and decimal prefixes for most other uses. Despite the IEC's 1998 International Standard creating several new binary prefixes (e.g. mebi-, kibi-) to distinguish the meaning of the decimal SI prefixes (e.g. mega- and kilo-, meaning 106 and 103 respectively) from the binary ones, and the subsequent incorporation of these IEC prefixes into the International System of Quantities (ISQ), consensus on Wikipedia in computing-related contexts currently favours the retention of the more familiar but ambiguous units "KB", "MB", "GB", "TB", "PB", "EB", etc. over use of unambiguous IEC binary prefixes. For detailed discussion, see Complete rewrite of Units of Measurements (June 2008).